1. Field of the Invention
The present invention relates to a hydraulic forming process for performing a hydraulic forming by increasing fluid pressure of fluid filled in a sealed space without using a complicated device, and a device for this process as well as a metal separator for a fuel cell having convex sections formed by the hydraulic forming process.
2. Description of the Prior Arts
A hydraulic forming process disclosed, for example, in the following patent document 1 has conventionally been well-known. In this conventional hydraulic forming process, a blank holder firstly clamps a thin metal plate with fluid filled in a hollow section formed at a lower die. Then, an upper die having formed thereon a plurality of concave sections is lowered and fluid pressure is raised by a pressure pump, thereby preforming on the thin metal plate convex sections projecting into the concave sections formed on the upper die. Subsequently, the fluid pressure is decreased and the upper die is lowered to a predetermined position for clamping the thin metal plate between the concave sections on the upper die and the convex sections on the lower die, whereby predetermined convex shapes are transferred onto the thin metal plate by a pressing. Then, a hydraulic valve is completely opened to decrease the fluid pressure, so that the upper die rises to return to the original position. In this way, the execution of the above-mentioned processes can form a plurality of concavo-convex shapes on the surface of the thin metal plate according to the conventional hydraulic forming process. This conventional hydraulic forming process is applied to a metal separator for a fuel cell having formed thereon a plurality of concavo-convex shapes in an embodiment of the invention.
[Patent Document 1]
Japanese Unexamined Patent Application No. 2001-259752
However, the conventional hydraulic forming process requires to increase the fluid pressure by the pressure pump upon preforming the thin metal plate. Therefore, the pressure pump has to be provided at the hydraulic forming device, that makes the overall construction of the hydraulic forming device complicated and expensive.